This introductory chapter outlines the problematic and its solution. It articulates some of the main tenets of (radical, individual, social) constructivism. Against these tenets are set some of the phenomena that constructivism cannot explain; it articulates some of the reasons why constructivism cannot explain them, including the inherent, presupposed separation between body and mind. The problems include (a) the learning paradox as framed by Carl Bereiter in the 1980s, which questions the possibility of a cognitive system to construct something of higher complexity than its own; (b) the impossibility to aim at (intend) the construction of knowledge that is inherently unknown ("how can you aim at constructing knowledge when this knowledge itself is required for aiming at it?"); (c) the constitutive role of the lived body in knowing; (d) the role of passivity in learning from experience; and (e) the inherent otherness of knowledge (language) and self. I conclude by foreshadowing the inner coherence of the argument that unfolds in this book.